Well, this is your lucky day because I think I can clear it up for you and save you some cash for a bit
1. Your husband can drive your car or your parents' car or his own car in Ontario. IIRC, he is visiting you, not on a work permit or something else that makes him a resident of Ontario. Therefore, get him an International Driving Permit and you're done. You should be able to do it via mail with AAA (instructions here) ($15 plus shipping fees).
"If you are a visitor to Ontario and want to drive while you are here, you must be at least 16 years old and have a valid driver's licence from your own province, state or country. If you are from another country and visiting Ontario for more than three months, you need an International Driver's Permit from your own country."
http://www.mto.gov.on.ca/english/dandv/driver/handbook/section1.1.0.shtml
2. A Canadian resident should NOT drive a foreign-plated car (unless they rented a car from a commercial agency in the US, have permission from the rental agency, and rent it for max 30 days -> this exception is relatively new). So, if you are a resident of Ontario and not just visiting Ontario you shouldn't drive his car unless it's an emergency or you guys are taking goods in to Canada in his car in the most direct path from the border to your house. Ditto for your parents.
[the sources are long so I'm putting them at the end of the post for clarity]
3. Once he gets his PR card, when he lands he should simultaneously import his car (on his B4). For this, you will need permission from the title-holder to export the car from the US. That way he won't be a Canadian resident driving a non-Canadian car.
4. He's going to need a Canadian driver's license (DL) to register the car, so you may want to get the DL shortly before landing so that you save that step. Depending on what US state his US DL is issued by, he may need a driving record.
Ta-da. Questions?
* * *
Sources for components of #2:
Tourists can temporarily import cars, per D19-12-1
"RIV Program Exemptions
49. Vehicles are exempt from complying with the CMVSS
at the point of entry into Canada if they are imported under
one of the following conditions:
(a) the vehicles are 15 years old or older, or are buses
manufactured before January 1, 1971; the importer
must be able to demonstrate the age of the vehicle;
(b) the vehicles are entering temporarily with:
(1) visitors, for a period not exceeding 12 months;
temporary residents such as students studying at an
institution of learning, for the duration of their
studies in Canada; or individuals with valid work
permits/authorizations for employment for a period
not exceeding 36 months;"
D2-4-1's covers residents of Canada's use of non-Canadian plated cars:
"GUIDELINES AND
GENERAL INFORMATION
Residents of Canada
1. Residents of Canada may operate conveyances on
which duties have not been paid in Canada only in
accordance with the terms and conditions of tariff item
No. 9802.00.00 and the regulations made pursuant thereto.
Purpose of Importation
2. Conveyances imported temporarily under these
Regulations are admissible for personal transportation only
from the point of arrival to a specified destination in Canada
and return within 30 days, when the purpose of importation
is to transport personally owned goods into or out of
Canada.
3. Similarly, customs inspectors may permit importation
in instances where a resident is required, due to unforeseen
circumstances or emergency reasons, to utilize a
conveyance on which duties have not been paid for personal
transportation to reach a specified destination in Canada and
return.
4. Under no circumstances are conveyances admissible
under these Regulations for touring purposes or for other
leisure activities in Canada, nor is any local use permitted
(e.g., point to point movement in Canada).
5. Customs inspectors will grant free importation of a
conveyance under these Regulations only when satisfied
that the applicable conditions have been met."
...unless it's a rental and certain conditions are met
"Exception — temporary importation
(1.1) Sections 5 and 6 do not apply to a resident of Canada who imports a vehicle that is licensed in the United States if the vehicle is rented in the United States from a vehicle rental business and is being imported into Canada for non-commercial purposes.
Importer to remove vehicle from Canada
(1.2) A resident of Canada who imports a vehicle under subsection (1.1) shall remove the vehicle from Canada within a period of 30 days, or any other prescribed period, beginning on the day on which the vehicle is imported.
Rental business to remove vehicle from Canada
(1.3) If, within the period referred to in subsection (1.2), the resident of Canada delivers the vehicle to a vehicle rental business in Canada with the consent of the business, then the vehicle rental business shall remove the vehicle from Canada before the end of that period."
http://laws-lois.justice.gc.ca/eng/acts/M-10.01/page-3.html
and
" Canadian residents may, as of June 1, 2012, bring U.S. rental vehicles into Canada for non-commercial use for 30 days or less. This will not affect the safety of Canadian road users, because Canadian and American vehicle standards are similar, and the vehicles will be in Canada for short periods of time.
While these changes to the Motor Vehicle Safety Act (MVSA) will allow one-way and two way trips, residents of Canada may only deliver a vehicle to a vehicle rental business for a one-way trip, with the consent of the business.
Visitors to Canada may continue to bring rental vehicles from the United States into Canada. "
http://www.tc.gc.ca/eng/roadsafety/safevehicles-rental-usa-1302.htm
